The dengue virus and its notorious relative, the Zika virus, infect millions of people each year. Genomic studies of the Zika virus have provided valuable insights into this infectious disease and its impact on emerging outbreaks. Zika is a flavivirus transmitted by mosquitoes, with most human infections being asymptomatic or presenting mild symptoms such as fever, rash, and joint pain.
The Zika virus gained worldwide attention during the 2015-2018 outbreak in the Americas, marked by a sharp increase in cases of microcephaly in newborns. This prompted the World Health Organization to declare it a global health emergency in 2016. Originating from Africa, the Zika virus has since spread to Asia, the Pacific islands, and the Americas. In recent years, there have been multiple outbreaks in Indian states like Kerala and Karnataka.
The virus was first isolated from monkeys in the Zika forest in Uganda in 1947, with the first human cases detected in Uganda and Tanzania in 1952. While there have been various outbreaks around the world, they have mostly been confined to tropical regions. The Zika virus’s genome has provided significant insights into the disease. Researchers sequenced the complete genome in 2007, revealing over 10,000 bases of single-stranded RNA. One unique aspect of the genome is that it encodes a large polyprotein, which is further cleaved into capsid, membrane precursor (prM), envelope, and seven non-structural proteins.
Diagnosing a Zika virus infection primarily relies on genetic testing due to the complexity of developing an antibody-based test. Antibodies produced during a Zika infection can cross-react with those of other viruses like dengue, yellow fever, and West Nile, making diagnosis challenging.
Epidemiology and surveillance play crucial roles in tracking Zika virus outbreaks. The virus’s RNA genome has a high potential for accumulating mutations, making it essential to apply the tools, techniques, and modalities we have developed to understand its evolution, genetic epidemiology, transmission, and pathogenesis. Genomic studies have revealed that the Zika virus has two lineages: African and Asian. The sub-lineage responsible for the devastating outbreak in the Americas is similar to isolates from a 2013-2014 outbreak in French Polynesia.
Genetic surveillance has proven invaluable in uncovering hidden outbreaks. For example, researchers in the U.S. used active surveillance of travelers to identify a concealed Zika outbreak in Cuba and determine its timeline. This kind of surveillance provides critical information for outbreak response strategies.
Microcephaly, characterized by abnormally small heads in infants, is one of the most alarming complications associated with Zika virus infection. Previous studies with mice suggested that a mutation in the precursor membrane protein (prM) of the Zika virus was linked to microcephaly. This mutation was believed to have emerged during the French Polynesia outbreak before spreading to South America. However, while the outbreak in South America involved virus lineages with this mutation, only some cases resulted in microcephaly. Researchers are still exploring the molecular mechanisms that contribute to microcephaly.
Recent studies conducted with primates indicate that fetal Zika virus infections are associated with high viral loads during pregnancy, which strongly influence fetal growth. Another study suggested that preexisting antibodies against dengue virus (DENV) can worsen the severity of congenital Zika virus infection. These findings highlight the importance of viral load and DENV infections in the development of microcephaly.
The interplay between Zika virus and the dengue virus has also been an area of interest. Evidence suggests that a Zika virus infection can increase the risk of severe dengue. Researchers exposed a large cohort of individuals in Nicaragua to both viruses sequentially and found that intermediate levels of anti-DENV antibodies resulting from prior Zika or DENV infection could significantly enhance the severity of dengue infections. This observation has significant public health implications, considering the global circulation of Zika and dengue, and could inform the development of Zika vaccines.
As climate change continues to influence the spread of vector-borne diseases and global warming creates more favorable environmental conditions for these diseases, our understanding of their molecular pathogenesis through genomic technologies is critical. These insights can guide effective measures for disease control and prevention.
In a recent study published in Cell, researchers from Tsinghua University demonstrated the interplay between Zika and dengue viruses and the specific microbes that grow on the skin. They found that infections with both viruses in primates suppressed an antimicrobial peptide on the skin, leading to the growth of specific microbes that produce volatile molecules called acetophenones. These molecules act as chemical cues to attract mosquitoes, facilitating the transmission of the viruses. The researchers also discovered that administering isotretinoin could reverse this phenomenon by upregulating the antimicrobial peptide.
Overall, the Zika virus and its interactions with other viruses continue to be incredibly fascinating subjects of research. By deepening our understanding of these infectious diseases at a molecular level, we can develop more effective strategies to combat their spread. As we face the challenges posed by climate change, our genomic technologies and insights will serve as invaluable tools in guiding public health efforts.
